The invention relates to apparatus for actuating exciting coils of electromagnetic switchgear using an on-off switch and a capacitor that is connected in parallel with the actuating voltage.
Siemens Catalog NS2 (January 1974), discloses a circuit arrangement in which in order to obtain a long break delay, for example for bridging brief voltage interruptions in the control circuit, an energy accumulator in the form of a capacitor is connected parallel to the circuit breaker coil. This capacitor, upon failure of the control voltage, discharges through the coil so that the circuit breaker magnetic remains closed for a prolonged period of time. To obtain reproducible switching times the capacitor must be charged with d-c voltage. Furthermore, for reasons of a sufficient time constant, a circuit breaker-driving magnet system which is suitable for d-c operation even without wiring, must be used in the the discharge loop.
However, when the above circuit arrangement is used with circuit breakers already in service it is impossible in a-c controls to increase the opening delay simply by adding a component, because a-c systems have too small a resistance for d-c actuation and therefore, also a time constant which is insufficient for the discharge.